User equipment involved in performing a random access procedure

ABSTRACT

The present disclosure relates to a user equipment (UE) that comprises a receiver, which receives a plurality of random access type threshold values. A processing circuitry of the UE determines a random value and then selects a type of a random access procedure to be performed by the UE. The selecting comprises at least selecting one out of the plurality of random access type threshold values, comparing the determined random value against the selected random access type threshold value, and selecting a type of the random access procedure based on the result of the comparison. The UE then performs the random access procedure of the selected type.

BACKGROUND Technical Field

The present disclosure is directed to methods, devices and articles incommunication systems, such as 3GPP communication systems.

Description of the Related Art

Currently, the 3rd Generation Partnership Project (3GPP) works at thetechnical specifications for the next generation cellular technology,which is also called fifth generation (5G).

One objective is to provide a single technical framework addressing allusage scenarios, requirements and deployment scenarios (see, e.g.,section 6 of TR 38.913 version 15.0.0), at least including enhancedmobile broadband (eMBB), ultra-reliable low-latency communications(URLLC), massive machine type communication (mMTC). For example, eMBBdeployment scenarios may include indoor hotspot, dense urban, rural,urban macro and high speed; URLLC deployment scenarios may includeindustrial control systems, mobile health care (remote monitoring,diagnosis and treatment), real time control of vehicles, wide areamonitoring and control systems for smart grids; mMTC deploymentscenarios may include scenarios with large number of devices withnon-time critical data transfers such as smart wearables and sensornetworks. The services eMBB and URLLC are similar in that they bothdemand a very broad bandwidth, however are different in that the URLLCservice may preferably require ultra-low latencies.

A second objective is to achieve forward compatibility. Backwardcompatibility to Long Term Evolution (LTE, LTE-A) cellular systems isnot required, which facilitates a completely new system design and/orthe introduction of novel features.

BRIEF SUMMARY

One non-limiting and exemplary embodiment facilitates providingprocedures for facilitating to improve the random access procedureperformed by a UE.

In an embodiment, the techniques disclosed here feature a user equipmentcomprising a receiver, which in operation, receives a plurality ofrandom access type threshold values. The UE also comprises processingcircuitry, which in operation, determines a random value. The processingcircuitry selects a type of a random access procedure to be performed bythe UE, wherein the selecting comprises at least

-   -   selecting one out of the plurality of random access type        threshold values,    -   comparing the determined random value against the selected        random access type threshold value, and    -   selecting a type of the random access procedure based on the        result of the comparison.

The UE then performs the random access procedure of the selected type.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments anddifferent implementations will be apparent from the specification andfigures. The benefits and/or advantages may be individually obtained bythe various embodiments and features of the specification and drawings,which need not all be provided in order to obtain one or more of suchbenefits and/or advantages.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the following exemplary embodiments are described in more detail withreference to the attached figures and drawings.

FIG. 1 shows an exemplary architecture for a 3GPP NR system;

FIG. 2 shows an exemplary user and control plane architecture for theLTE eNB, gNB, and UE,

FIG. 3 is a schematic drawing which shows a functional split betweenNG-RAN and 5GC,

FIG. 4 is a sequence diagram for RRC connection setup/reconfigurationprocedures,

FIG. 5 is a schematic drawing showing usage scenarios of Enhanced mobilebroadband (eMBB), Massive Machine Type Communications (mMTC) and UltraReliable and Low Latency Communications (URLLC),

FIG. 6 is a block diagram showing an exemplary 5G system architecturefor a non-roaming scenario,

FIG. 7 illustrates the messages exchanged between an eNB and a UE whenperforming a contention-based RACH procedure;

FIG. 8 illustrates the messages exchanged between an eNB and a UE whenperforming a contention-free RACH procedure;

FIG. 9 illustrates the exemplary and simplified structure of a UE and agNB:

FIG. 10 illustrates a structure of the UE according to an exemplaryimplementation of an improved random access procedure;

FIG. 11 is a flow diagram for the behavior of a UE, according to anexemplary implementation for an improved solution,

FIG. 12 is a flow diagram for the behavior of a gNB, according to anexemplary implementation for an improved solution,

FIG. 13 is a flow diagram for the behavior of a UE, according to anexemplary implementation for an improved solution,

FIG. 14 is a flow diagram for the behavior of a UE, according to anexemplary implementation for an improved solution, and

FIG. 15 is a flow diagram for the behavior of a gNB, according to anexemplary implementation for an improved solution.

DETAILED DESCRIPTION 5G NR System Architecture and Protocol Stacks

3GPP has been working at the next release for the 5^(th) generationcellular technology, simply called 5G, including the development of anew radio access technology (NR) operating in frequencies ranging up to100 GHz. The first version of the 5G standard was completed at the endof 2017, which allows proceeding to 5G NR standard-compliant trials andcommercial deployments of smartphones.

Among other things, the overall system architecture assumes an NG-RAN(Next Generation-Radio Access Network) that comprises gNBs, providingthe NG-radio access user plane (SDAP/PDCP/RLC/MAC/PHY) and control plane(RRC) protocol terminations towards the UE. The gNBs are interconnectedwith each other by means of the Xn interface. The gNBs are alsoconnected by means of the Next Generation (NG) interface to the NGC(Next Generation Core), more specifically to the AMF (Access andMobility Management Function) (e.g., a particular core entity performingthe AMF) by means of the NG-C interface and to the UPF (User PlaneFunction) (e.g., a particular core entity performing the UPF) by meansof the NG-U interface. The NG-RAN architecture is illustrated in FIG. 1(see, e.g., 3GPP TS 38.300 v15.6.0, section 4).

Various different deployment scenarios can be supported (see, e.g., 3GPPTR 38.801 v14.0.0). For instance, a non-centralized deployment scenario(see, e.g., section 5.2 of TR 38.801; a centralized deployment isillustrated in section 5.4) is presented therein, where base stationssupporting the 5G NR can be deployed. FIG. 2 illustrates an exemplarynon-centralized deployment scenario (see, e.g., FIG. 5.2.-1 of said TR38.801), while additionally illustrating an LTE eNB as well as a userequipment (UE) that is connected to both a gNB and an LTE eNB. The neweNB for NR 5G may be exemplarily called gNB. An eLTE eNB is theevolution of an eNB that supports connectivity to the EPC (EvolvedPacket Core) and the NGC (Next Generation Core).

The user plane protocol stack for NR (see, e.g., 3GPP TS 38.300, section4.4.1) comprises the PDCP (Packet Data Convergence Protocol, see section6.4 of TS 38.300), RLC (Radio Link Control, see section 6.3 of TS38.300) and MAC (Medium Access Control, see section 6.2 of TS 38.300)sublayers, which are terminated in the gNB on the network side.Additionally, a new access stratum (AS) sublayer (SDAP, Service DataAdaptation Protocol) is introduced above PDCP (see, e.g., sub-clause 6.5of 3GPP TS 38.300). A control plane protocol stack is also defined forNR (see for instance TS 38.300, section 4.4.2). An overview of the Layer2 functions is given in sub-clause 6 of TS 38.300. The functions of thePDCP, RLC and MAC sublayers are listed respectively in sections 6.4,6.3, and 6.2 of TS 38.300. The functions of the RRC layer are listed insub-clause 7 of TS 38.300.

For instance, the Medium-Access-Control layer handles logical-channelmultiplexing, and scheduling and scheduling-related functions, includinghandling of different numerologies.

The physical layer (PHY) is for example responsible for coding, PHY HARQprocessing, modulation, multi-antenna processing, and mapping of thesignal to the appropriate physical time-frequency resources. It alsohandles mapping of transport channels to physical channels. The physicallayer provides services to the MAC layer in the form of transportchannels. A physical channel corresponds to the set of time-frequencyresources used for transmission of a particular transport channel, andeach transport channel is mapped to a corresponding physical channel.One physical channel is the PRACH (Physical Random Access Channel) usedfor the random access.

Use cases/deployment scenarios for NR could include enhanced mobilebroadband (eMBB), ultra-reliable low-latency communications (URLLC),massive machine type communication (mMTC), which have diverserequirements in terms of data rates, latency, and coverage. For example,eMBB is expected to support peak data rates (20 Gbps for downlink and 10Gbps for uplink) and user-experienced data rates in the order of threetimes what is offered by IMT-Advanced. On the other hand, in case ofURLLC, the tighter requirements are put on ultra-low latency (0.5 ms forUL and DL each for user plane latency) and high reliability (1-10⁻⁵within 1 ms). Finally, mMTC may preferably require high connectiondensity (1,000,000 devices/km² in an urban environment), large coveragein harsh environments, and extremely long-life battery for low costdevices (15 years).

Therefore, the OFDM numerology (e.g., subcarrier spacing, OFDM symbolduration, cyclic prefix (CP) duration, number of symbols per schedulinginterval) that is suitable for one use case might not work well foranother. For example, low-latency services may preferably require ashorter symbol duration (and thus larger subcarrier spacing) and/orfewer symbols per scheduling interval (aka, TTI) than an mMTC service.Furthermore, deployment scenarios with large channel delay spreads maypreferably require a longer CP duration than scenarios with short delayspreads. The subcarrier spacing should be optimized accordingly toretain the similar CP overhead. NR may support more than one value ofsubcarrier spacing. Correspondingly, subcarrier spacing of 15 kHz, 30kHz, 60 kHz . . . are being considered at the moment. The symbolduration T_(u) and the subcarrier spacing Δf are directly relatedthrough the formula Δf=1/T_(u). In a similar manner as in LTE systems,the term “resource element” can be used to denote a minimum resourceunit being composed of one subcarrier for the length of one OFDM/SC-FDMAsymbol.

In the new radio system 5G-NR for each numerology and carrier a resourcegrid of subcarriers and OFDM symbols is defined respectively for uplinkand downlink. Each element in the resource grid is called a resourceelement and is identified based on the frequency index in the frequencydomain and the symbol position in the time domain (see 3GPP TS 38.211v15.6.0).

5G NR Functional Split Between NG-RAN and 5GC

FIG. 3 illustrates functional split between NG-RAN and 5GC. NG-RANlogical node is a gNB or ng-eNB. The 5GC has logical nodes AMF, UPF andSMF.

In particular, the gNB and ng-eNB host the following main functions:

-   -   Functions for Radio Resource Management such as Radio Bearer        Control, Radio Admission Control, Connection Mobility Control,        Dynamic allocation of resources to UEs in both uplink and        downlink (scheduling);    -   IP header compression, encryption and integrity protection of        data;    -   Selection of an AMF at UE attachment when no routing to an AMF        can be determined from the information provided by the UE;    -   Routing of User Plane data towards UPF(s);    -   Routing of Control Plane information towards AMF;    -   Connection setup and release;    -   Scheduling and transmission of paging messages;    -   Scheduling and transmission of system broadcast information        (originated from the AMF or OAM);    -   Measurement and measurement reporting configuration for mobility        and scheduling;    -   Transport level packet marking in the uplink;    -   Session Management;    -   Support of Network Slicing;    -   QoS Flow management and mapping to data radio bearers;    -   Support of UEs in RRC_INACTIVE state;    -   Distribution function for NAS messages;    -   Radio access network sharing;    -   Dual Connectivity;    -   Tight interworking between NR and E-UTRA.

The Access and Mobility Management Function (AMF) hosts the followingmain functions:

-   -   Non-Access Stratum, NAS, signaling termination;    -   NAS signaling security;    -   Access Stratum, AS, Security control;    -   Inter Core Network, CN, node signaling for mobility between 3GPP        access networks;    -   Idle mode UE Reachability (including control and execution of        paging retransmission);    -   Registration Area management;    -   Support of intra-system and inter-system mobility;    -   Access Authentication;    -   Access Authorization including check of roaming rights;    -   Mobility management control (subscription and policies);    -   Support of Network Slicing;    -   Session Management Function, SMF, selection.

Furthermore, the User Plane Function, UPF, hosts the following mainfunctions:

-   -   Anchor point for Intra-/Inter-RAT mobility (when applicable);    -   External PDU session point of interconnect to Data Network;    -   Packet routing & forwarding;    -   Packet inspection and User plane part of Policy rule        enforcement;    -   Traffic usage reporting;    -   Uplink classifier to support routing traffic flows to a data        network;    -   Branching point to support multi-homed PDU session;    -   QoS handling for user plane, e.g., packet filtering, gating,        UL/DL rate enforcement;    -   Uplink Traffic verification (SDF to QoS flow mapping);    -   Downlink packet buffering and downlink data notification        triggering.

Finally, the Session Management function, SMF, hosts the following mainfunctions.

-   -   Session Management;    -   UE IP address allocation and management;    -   Selection and control of UP function;    -   Configures traffic steering at User Plane Function, UPF, to        route traffic to proper destination;    -   Control part of policy enforcement and QoS;    -   Downlink Data Notification.

RRC Connection Setup and Reconfiguration Procedures

FIG. 4 illustrates some interactions between a UE, gNB, and AMF (an 5GCentity) in the context of a transition of the UE from RRC_IDLE toRRC_CONNECTED for the NAS part (see TS 38.300 v15.6.0).

RRC is a higher layer signaling (protocol) used for UE and gNBconfiguration. In particular, this transition involves that the AMFprepares the UE context data (including, e.g., PDU session context, theSecurity Key, UE Radio Capability and UE Security Capabilities, etc.)and sends it to the gNB with the INITIAL CONTEXT SETUP REQUEST. Then,the gNB activates the AS security with the UE, which is performed by thegNB transmitting to the UE a SecurityModeCommand message and by the UEresponding to the gNB with the SecurityModeComplete message. Afterwards,the gNB performs the reconfiguration to setup the Signaling Radio Bearer2, SRB2, and Data Radio Bearer(s), DRB(s) by means of transmitting tothe UE the RRCReconfiguration message and, in response, receiving by thegNB the RRCReconfigurationComplete from the UE. For a signaling-onlyconnection, the steps relating to the RRCReconfiguration are skippedsince SRB2 and DRBs are not setup. Finally, the gNB informs the AMF thatthe setup procedure is completed with the INITIAL CONTEXT SETUPRESPONSE.

In the present disclosure, thus, an entity (for example AMF, SMF, etc.)of a 5th Generation Core (5GC) is provided that comprises controlcircuitry which, in operation, establishes a Next Generation (NG)connection with a gNodeB, and a transmitter which, in operation,transmits an initial context setup message, via the NG connection, tothe gNodeB to cause a signaling radio bearer setup between the gNodeBand a user equipment (UE). In particular, the gNodeB transmits a RadioResource Control, RRC, signaling containing a resource allocationconfiguration information element to the UE via the signaling radiobearer. The UE then performs an uplink transmission or a downlinkreception based on the resource allocation configuration.

Usage Scenarios of IMT for 2020 and Beyond

FIG. 5 illustrates some of the use cases for 5G NR. In 3rd generationpartnership project new radio (3GPP NR), three use cases are beingconsidered that have been envisaged to support a wide variety ofservices and applications by IMT-2020. The specification for the phase 1of enhanced mobile-broadband (eMBB) has been concluded. In addition tofurther extending the eMBB support, the current and future work wouldinvolve the standardization for ultra-reliable and low-latencycommunications (URLLC) and massive machine-type communications. FIG. 5illustrates some examples of envisioned usage scenarios for IMT for 2020and beyond.

The URLLC use case has stringent requirements for capabilities such asthroughput, latency and availability and has been envisioned as one ofthe enablers for future vertical applications such as wireless controlof industrial manufacturing or production processes, remote medicalsurgery, distribution automation in a smart grid, transportation safety,etc. Ultra-reliability for URLLC is to be supported by identifying thetechniques to meet the requirements set by TR 38.913. For NR URLLC inRelease 15, key requirements include a target user plane latency of 0.5ms for UL (uplink) and 0.5 ms for DL (downlink). The general URLLCrequirement for one transmission of a packet is a BLER (block errorrate) of 1E-5 for a packet size of 32 bytes with a user plane latency of1 ms.

From RAN1 perspective, reliability can be improved in a number ofpossible ways. The current scope for improving the reliability involvesdefining separate CQI tables for URLLC, more compact DCI formats,repetition of PDCCH, etc. However, the scope may widen for achievingultra-reliability as the NR becomes more stable and developed (for NRURLLC key requirements). Particular use cases of NR URLCC in Rel. 15include Augmented Reality/Virtual Reality (AR/VR), e-health, e-safety,and mission-critical applications.

Moreover, technology enhancements targeted by NR URLCC aim at latencyimprovement and reliability improvement. Technology enhancements forlatency improvement include configurable numerology, non slot-basedscheduling with flexible mapping, grant free (configured grant) uplink,slot-level repetition for data channels, and downlink pre-emption.Pre-emption means that a transmission for which resources have alreadybeen allocated is stopped, and the already allocated resources are usedfor another transmission that has been requested later, but has lowerlatency/higher priority requirements. Accordingly, the already grantedtransmission is pre-empted by a later transmission. Pre-emption isapplicable independent of the particular service type. For example, atransmission for a service-type A (URLCC) may be pre-empted by atransmission for a service type B (such as eMBB). Technologyenhancements with respect to reliability improvement include dedicatedCQI/MCS tables for the target BLER of 1E-5.

The use case of mMTC (massive machine type communication) ischaracterized by a very large number of connected devices typicallytransmitting a relatively low volume of non-delay sensitive data.Devices are required to be low cost and to have a very long batterylife. From NR perspective, utilizing very narrow bandwidth parts is onepossible solution to have power saving from UE perspective and enablelong battery life.

As mentioned above, it is expected that the scope of reliability in NRbecomes wider. One key requirement to all the cases, and especiallynecessary for URLLC and mMTC, is high reliability or ultra-reliability.Several mechanisms can be considered to improve the reliability fromradio perspective and network perspective. In general, there are a fewkey potential areas that can help improve the reliability. Among theseareas are compact control channel information, data/control channelrepetition, and diversity with respect to frequency, time and/or thespatial domain. These areas are applicable to reliability in general,regardless of particular communication scenarios.

For NR URLLC, further use cases with tighter requirements have beenidentified such as factory automation, transport industry and electricalpower distribution, including factory automation, transport industry,and electrical power distribution. The tighter requirements are higherreliability (up to 10-6 level), higher availability, packet sizes of upto 256 bytes, time synchronization down to the order of a few μs wherethe value can be one or a few μs depending on frequency range and shortlatency in the order of 0.5 to 1 ms in particular a target user planelatency of 0.5 ms, depending on the use cases.

Moreover, for NR URLLC, several technology enhancements from RAN1perspective have been identified. Among these are PDCCH (PhysicalDownlink Control Channel) enhancements related to compact DCI, PDCCHrepetition, increased PDCCH monitoring. Moreover, UCI (Uplink ControlInformation) enhancements are related to enhanced HARQ (Hybrid AutomaticRepeat Request) and CSI feedback enhancements. Also PUSCH enhancementsrelated to mini-slot level hopping and retransmission/repetitionenhancements have been identified. The term “mini-slot” refers to aTransmission Time Interval (TTI) including a smaller number of symbolsthan a slot (a slot comprising fourteen symbols).

QoS Control

The 5G QoS (Quality of Service) model is based on QoS flows and supportsboth QoS flows that require guaranteed flow bit rate (GBR QoS flows) andQoS flows that do not require guaranteed flow bit rate (non-GBR QoSFlows). At NAS level, the QoS flow is thus the finest granularity of QoSdifferentiation in a PDU session. A QoS flow is identified within a PDUsession by a QoS flow ID (QFI) carried in an encapsulation header overNG-U interface.

For each UE, 5GC establishes one or more PDU Sessions. For each UE, theNG-RAN establishes at least one Data Radio Bearers (DRB) together withthe PDU Session, and additional DRB(s) for QoS flow(s) of that PDUsession can be subsequently configured (it is up to NG-RAN when to doso), e.g., as shown above with reference to FIG. 4. The NG-RAN mapspackets belonging to different PDU sessions to different DRBs. NAS levelpacket filters in the UE and in the 5GC associate UL and DL packets withQoS Flows, whereas AS-level mapping rules in the UE and in the NG-RANassociate UL and DL QoS Flows with DRBs.

FIG. 6 illustrates a 5G NR non-roaming reference architecture (see TS23.501 v16.1.0, section 4.23). An Application Function (AF), e.g., anexternal application server hosting 5G services, exemplarily describedin FIG. 5, interacts with the 3GPP Core Network in order to provideservices, for example to support application influence on trafficrouting, accessing Network Exposure Function (NEF) or interacting withthe Policy framework for policy control (see Policy Control Function,PCF), e.g., QoS control. Based on operator deployment, ApplicationFunctions considered to be trusted by the operator can be allowed tointeract directly with relevant Network Functions. Application Functionsnot allowed by the operator to access directly the Network Functions usethe external exposure framework via the NEF to interact with relevantNetwork Functions.

FIG. 6 shows further functional units of the 5G architecture, namelyNetwork Slice Selection Function (NSSF), Network Repository Function(NRF), Unified Data Management (UDM), Authentication Server Function(AUSF), Access and Mobility Management Function (AMF), SessionManagement Function (SMF), and Data Network (DN), e.g., operatorservices, Internet access or 3rd party services.

Unified Access Control (UAC)

In the exemplary 5G scenarios, different criterion can be used indetermining which access attempt should be allowed or blocked, e.g.,depending on operator policies, deployment scenarios, subscriberprofiles, and available services (see 3GPP TS 22.261 v16.8.0 section6.22, 3GPP TS 24.501 v16.1.0 section 4.5). These different criteria foraccess control can be associated with Access Identities and AccessCategories. The 5G system currently provides a single unified accesscontrol where operators control accesses based on these two criterions.

In unified access control, each access attempt is categorized into oneor more of the Access Identities and one of the Access Categories. Basedon the access control information applicable for the correspondingAccess Identity and Access Category of the access attempt, the UEperforms a test whether the actual access attempt can be made or not.

The unified access control supports extensibility to allow inclusion ofadditional standardized Access Identities and Access Categories andsupports flexibility to allow operators to define operator-definedAccess Categories using their own criterion (e.g., network slicing,application, and application server).

The following table gives an overview of the different Access Identitiesthat could be defined in 3GPP.

Access Identity number UE configuration 0 UE is not configured with anyparameters from this table 1 (NOTE 1) UE is configured for MultimediaPriority Service (MPS). 2 (NOTE 2) UE is configured for Mission CriticalService (MCS). 3-10 Reserved for future use 11 (NOTE 3) Access Class 11is configured in the UE. 12 (NOTE 3) Access Class 12 is configured inthe UE. 13 (NOTE 3) Access Class 13 is configured in the UE. 14 (NOTE 3)Access Class 14 is configured in the UE. 15 (NOTE 3) Access Class 15 isconfigured in the UE. NOTE 1: Access Identity 1 is used by UEsconfigured for MPS, in the PLMNs where the configuration is valid. ThePLMNs where the configuration is valid are HPLMN, PLMNs equivalent toHPLMN, and visited PLMNs of the home country. Access Identity I is alsovalid when the UE is explicitly authorized by the network based onspecific configured PLMNs inside and outside the home country. NOTE 2:Access Identity 2 is used by UEs configured for MCS, in the PLMNs wherethe configuration is valid. The PLMNs where the configuration is validare HPLMN or PLMNs equivalent to HPLMN and visited PLMNs of the homecountry. Access Identity 2 is also valid when the UE is explicitlyauthorized by the network based on specific configured PLMNs inside andoutside the home country. NOTE 3: Access Identities 11 and 15 are validin Home PLMN only if the EHPLMN list is not present or in any EHPLMN.Access Identities 12, 13 and 14 are valid in Home PLMN and visited PLMNsof home country only. For this purpose, the home country is defined asthe country of the MCC part of the IMSI.

The following table gives an overview of the different Access Categoriesthat could be defined in 3GPP.

Access Category number Conditions related to UE Type of access attempt 0All MO (Mobile Originated) signaling resulting from paging 1 (NOTE 1) UEis configured for delay tolerant service All except for Emergency andsubject to access control for Access Category 1, which is judged basedon relation of UE's HPLMN and the selected PLMN. 2 All Emergency 3 Allexcept for the conditions in Access MO signaling on NAS levelCategory 1. resulting from other than paging 4 All except for theconditions in Access MMTEL voice (NOTE 3) Category 1. 5 All except forthe conditions in Access MMTEL video Category 1. 6 All except for theconditions in Access SMS Category 1. 7 All except for the conditions inAccess MO data that do not belong to any Category 1. other AccessCategories (NOTE 4) 8 All except for the conditions in Access MOsignaling on RRC level Category 1 resulting from other than paging 9-31Reserved standardized Access Categories 32-63 (NOTE 2) All Based onoperator classification NOTE 1: The barring parameter for AccessCategory 1 is accompanied with information that define whether AccessCategory applies to UEs within one of the following categories: a) UEsthat are configured for delay tolerant service; b) UEs that areconfigured for delay tolerant service and are neither in their HPLMN norin a PLMN that is equivalent to it; c) UEs that are configured for delaytolerant service and are neither in the PLMN listed as most preferredPLMN of the country where the UE is roaming in the operator-defined PLMNselector list on the SIM/USIM, nor in their HPLMN nor in a PLMN that isequivalent to their HPLMN. When a UE is configured for EAB, the UE isalso configured for delay tolerant service. In case a UE is configuredboth for EAB and for EAB override, when upper layer indicates tooverride Access Category 1, then Access Category 1 is not applicable.NOTE 2: When there are an Access Category based on operatorclassification and a standardized Access Category to both of which anaccess attempt can be categorized, and the standardized Access Categoryis neither 0 nor 2, the UE applies the Access Category based on operatorclassification. When there are an Access Category based on operatorclassification and a standardized Access Category to both of which anaccess attempt can be categorized, and the standardized Access Categoryis 0 or 2, the UE applies the standardized Access Category. NOTE 3:Includes Real-Time Text (RTT). NOTE 4: Includes IMS Messaging.

As apparent from the above table, Access Category 0 shall not be barred,irrespective of Access Identities.

Based on operator's policy, the 5G system shall be able to prevent UEsfrom accessing the network using relevant barring parameters that varydepending on the Access Identity and Access Category. Access Identitiesare configured at the UE as listed in the above table. Access Categoriesare defined by the combination of conditions related to UE and the typeof access attempt as listed in the above table. One or more AccessIdentities and only one Access Category are selected and tested for anaccess attempt.

The 5G network shall be able to broadcast barring control information(i.e., a list of barring parameters associated with an Access Identityand an Access Category) in one or more areas of the RAN.

The UE shall be able to determine whether or not a particular new accessattempt is allowed based on barring parameters that the UE receives fromthe broadcast barring control information and the configuration in theUE. The unified access control framework can be applicable to UEs in RRCIdle, RRC Inactive, and RRC Connected at the time of initiating a newaccess attempt (e.g., new session request).

In particular, the purpose of the UAC procedure is to perform an accessbarring check for an access attempt associated with a given AccessCategory and one or more Access Identities, e.g., upon request fromupper layers.

The Access control check is performed for access attempts of particularevents, e.g., as defined in 3GPP TS 24.501 v16.1.0 section 4.5.1. Whenthe UE wants to initiate an access attempt in one of these events, theUE can determine one or more access identities from the standardizedaccess identities (see above table), and one access category from theset of standardized access categories and possibly operator-definedaccess categories (see, e.g., TS 24.501, section 4.5.3), to beassociated with that access attempt.

In one exemplary 3GPP implementation, the following steps are performedby the UE in relation to the unified access control (UAC) procedure (see3GPP TS 38.331 v15.6.0 section 5.3.14.5):

The UE shall:

1> it: one or more Access identities are indicated according to TS24.501, and 1> if for at least one of these Access Identities thecorresponding bit in the uac-BarringForAccessIdentity contained in ″UACbarring parameter″ is set to zero: 2> consider the access attempt asallowed; 1> else: 2> draw a random number 'rand' uniformly distributedin the range: 0 ≤ rand <1; 2> if 'rand' is lower than the -valueindicated by uac-BarringFactor included ″UAC barring parameter″: 3>consider the access attempt as allowed; 2>else.: 3> consider the accessattempt as barred; 1> if the access attempt is considered as barred: 2>draw a random. number 'rand' that is uniformly distributed in the range0 d _rand <1; 2>start timer T390 for the Access Category with the timervalue calculated as follows, using the uac-Barringfrime included in ″ACbarring parameter″: T390 = (0.7+0.6 , * rand) * uac-BarringTime.

Some parameters for the UAC procedure are provided to the UE via SystemInformation, e.g., in the SIB1 (e.g., SIB1, see 3GPP TS 38.331 v15.6.0section 6.2.2).

-   -   SIB1 contains information relevant when evaluating if a UE is        allowed to access a cell and defines the scheduling of other        system information. It also contains radio resource        configuration information that is common for all UEs and barring        information applied to the unified access control.

Signaling radio bearer: N/A

RLC-SAP: TM

Logical channels: BCCH

Direction: Network to UE

SIB1 Message

-- ASN1START -- TAG-SIB1-START SIB1 ::= SEQUENCE {  cellSelectionInfo SEQUENCE {   q-RxLevMin     Q-RxLevMin,   q-RxLevMinOffset     INTEGER(1..8) OPTIONAL, -- Need S   q-RxLevklinSUL     Q-RxLevMin OPTIONAL, --Need R   q-QualMin     Q-QualMin OPTIONAL, -- Need S   q-QualMinOffset   INTEGER (1..8) OPTIONAL -- Need S  }        OPTIONAL, -- CondStandalone  cellAccessRelatedInfo    CellAccessRelatedInfo, connEstFailureControl    ConnEstFailureControl OPTIONAL, -- Need R si-SchedulingInfo    SI-SchedulingInfo OPTIONAL, -- Need R servingCellConfigCommon    ServingCellConfigCommonSIB OPTIONAL, -- NeedR  ims-ErnergeneySuppod     ENUMERATED {true} OPTIONAL, -- Need R eCallOverIMS-Support    ENUMERATED {true} OPTIONAL, -- Cond Absent ue-TimersAndConstants     UE-TimersAndConstants OPTIONAL, -- Need R uac-BarringInfo  SEQUENCE {   uac-BarringForCommon     UAC-BarringPerCatList OPTIONAL, -- Need S   oac-BarringPerPLMN-List     UAC-BarringPerPLMN-List OPTIONAL, -- Need S  uac-BarringInfoSetList      UAC-BarringInfoSetList,  uac-AccessCategory1-SeleetionAssistanceInfo CHOICE {    pimnCommon     UAC-AccessCategory1-SelectionAssistanceInfo,    individualPLMNList     SEQUENCE (SIZE (2..maxPLMN)) OF UAC-AccessCategory1-SelectionAssistanceInfo   }        OPTIONAL -- Need S  }       OPTIONAL, -- Need R  useFullResumeID   ENUMERATED{true} OPTIONAL, -- Need N  lateNonCriticalExtension    OCTETSTRING OPTIONAL,  nonCriticalExtension   SEQUENCE{} OPTIONAL }UAC-Accesseategory1-SelectionAssistanceInfo ::=       ENUMERATED {a, b,c} -- TAG-SIB1-STOP -- ASN1STOP

SIB1 field descriptions cellSelectionInfo Parameters for cell selectionrelated to the serving cell. ims-EmergencySupport Indicates whether thecell supports IMS emergency bearer services for UEs in limited servicemode. If absent, IMS emergency call is not supported by the network inthe cell for UEs in limited service mode. q-QualMin Parameter“Q_(qualmin)” in TS 38.304 [20], applicable for serving cell. If thefield is absent, the UE applies the (default) value of negative infinityfor Q_(qualmin). q-QualMinOffset Parameter “Q_(qualminoffset)” in TS38.304 [20]. Actual value Q_(qualminoffset) = field value [dB]. If thefield is absent, the UE applies the (default) value of 0 dB forQ_(qualminoffset). Affects the minimum required quality level in thecell. q-RxLevMin Parameter “Q_(rxlevmin)” in TS 38.304 [20], applicablefor serving cell. q-RxLevMinOffset Parameter “Q_(rxlevminoffset)” in TS38.304 [20]. Actual value Q_(rxlevminoffset) = field value * 2 [dB]. Ifabsent, the UE applies the (default) value of 0 dB forQ_(rxlevminoffset). Affects the minimum required Rx level in the cell.q-RxLevMinSUL Parameter “Q_(rxlevmin)” in TS 38.304 [20], applicable forserving cell. servingCellConfigCommon Configuration of the serving cell,uac-AccessCategory1-SelectionAssistanceInfo Information used todetermine whether Access Category 1 applies to the UE, as defined in TS22.261 [25]. uac-BarringForCommon Common access control parameters foreach access category. Common values are used for all PLMNs, unlessoverwritten by the PLMN specific configuration provided inuac-BarringPerPLMN-List. The parameters are specified by providing anindex to the set of configurations (uac-BarringInfoSetList). UE behaviorupon absence of this field is specified in clause 5.3.14.2.ue-TimersAndConstants Timer and constant values to be used by the UE.useFullResumeID Indicates which resume identifier and Resume requestmessage should be used. UE uses fullI-RNTI and RRCResumeRequest1 if thefield is present, or shortI-RNTI and RRCResumeRequest if the field isabsent. Conditional Presence Explanation Absent The field is not used inthis version of the specification if received the UE shall ignore.Standalone The field is mandatory present in a cell that supportsstandalone operation, otherwise it is absent.

The parameter UAC-BarringInfoSetList of SIB1 can be defined as followsand carries the parameter UAC-BarringFactor mentioned above in the UACprocedure.

UAC-BarringInfoSetList

The IE UAC-BarringInfoSetList provides a list of access controlparameter sets. An access category can be configured with accessparameters according to one of the sets.

UAC-BarringInfoSetList Information Element

-- ASN1START -- TAG-UAC-BARRINGINFOSETLIST-START UAC-BarringInfoSetList::=  SEQUENCE {SIZE(1..maxBarringInfoSet) ) OF      UAC-     BarringInfoSet UAC-BarringInfoSet ::=  SEQUENCE { uac-BarringFactorENUMERATED {p00, p05, p10, p15, p20, p25,    p30, p40, p50, p60, p70,p75,    p80, p85, p90, p95} , uac-BarringTime ENUMERATED {s4, s8, s16,s32, s64, s128,     s256, s512}, uac-BarringForAccessIdentity   BITSTRING (SIZE (7) ) } -- TAG-UAC-BARRINGINFOSETLIST-STOP -- ASN1STOP

UAC-BarringInfoSetList field descriptions uac-BarringInfoSetList List ofaccess control parameter sets. Each access category can be configuredwith access parameters corresponding to a particular set byuac-barringInfoSetIndex. Association of an access category with an indexthat has no corresponding entry in the uac-BarringInfoSetList is validconfiguration and indicates no barring, uac-BarringForAccessIdentityIndicates whether access attempt is allowed for each Access Identity.The leftmost bit, bit 0 in the bit string corresponds to Access Identity1, bit 1 in the bit string corresponds to Access Identity 2, bit 2 inthe bit string corresponds to Access Identity 11, bit 3 in the bitstring corresponds to Access Identity 12, bit 4 in the bit stringcorresponds to Access Identity 13, bit 5 in the bit string correspondsto Access Identity 14, and bit 6 in the bit string corresponds to AccessIdentity 15. Value 0 means that access attempt is allowed for thecorresponding access identity. uac-BarringFactor Represents theprobability that access attempt would be allowed during access barringcheck. uac-BarringFactor The minimum time in seconds before a new accessattempt is to be performed after an access attempt was barred at accessbarring check for the same access category.

The above UAC procedure can be summarized as follows. It is assumed thatan access attempt can be associated to one Access Category and one ormore Access identities. The UE first checks whether the access attemptis allowed based on the associated Access Identities and the configuredAccess Identities broadcast by system information (e.g., SIB1, see 3GPPTS 38.331 v15.6.0 section 6.2.2). Then, if the UE determines, based onthe access identity(ies), it is allowed to perform an access attemptwith the cell, the UE then proceeds to perform the access attempt. Onthe other hand, if the UE determines, based on the access identity(ies),that it is not allowed to perform an access attempt with the cell, theUE then proceeds to determine whether an access attempt is allowed basedon the access category. This, for instance, involves drawing a randomvalue and comparing same with a particular probability threshold for theaccess-category-based access attempt (uac-BarringFactor associated withthat access category; information is known to the UE, e.g., by systeminformation). If the random value is less than the access attemptprobability threshold, then the UE is allowed to access the cell. But,if the random value is equal to or larger than the access attemptprobability threshold, the UE is not allowed to access the cell.

One important further procedure performed at the UE that is closelyrelated to the Unified Access Control is the random access procedure(also termed RACH procedure). UAC allows the UE to test whether the UEshould perform an access attempt with a particular gNB. Once the UEpositively decides to perform an access attempt, the UE may for instanceperform a random access procedure to access the radio cell; putdifferently, an access attempt involves performing a random accessprocedure.

As will be described in the following, a random access procedure can beperformed for many different reasons. From the perspective of the RACHprocedure, performing a random access procedure may or may not always bepreceded by the UE performing a UAC check as described above.

Random Access Procedure

Similar to LTE, 5G NR provides a RACH (Random Access Channel) procedure(or simply random access procedure). For instance, the RACH procedurecan be used by the UE to access a cell it has found. The RACH procedurecan also be used in other contexts within NR, for example:

-   -   For handover, when synchronization is to be established to a new        cell;    -   To reestablish uplink synchronization to the current cell if        synchronization has been lost due to a too long period without        any uplink transmission from the device;    -   To request uplink scheduling if no dedicated scheduling request        resource has been configured for the device.

There are numerous events that may trigger the UE to perform a randomaccess procedure such as (see 3GPP TS 38.300, v15.6.0 section 9.2.6):

-   -   Initial access from RRC_IDLE;    -   RRC Connection Re-establishment procedure;    -   DL or UL data arrival during RRC_CONNECTED when UL        synchronization status is “non-synchronized”;    -   UL data arrival during RRC_CONNECTED when there are no PUCCH        resources for SR available;    -   SR failure;    -   Request by RRC upon synchronous reconfiguration (e.g.,        handover);    -   Transition from RRC_INACTIVE;    -   To establish time alignment at SCell addition;    -   Request for Other SI (see subclause 7.3);    -   Beam failure recovery.

The RACH procedure will be described in the following in more detail,with reference to FIGS. 7 and 8. A mobile terminal can be scheduled foruplink transmission, if its uplink transmission is time synchronized.Therefore, the Random Access Channel (RACH) procedure plays a role as aninterface between non-synchronized mobile terminals (UEs) and theorthogonal transmission of the uplink radio access. For instance, theRandom Access is used to achieve uplink time synchronization for a userequipment, which either has not yet acquired, or has lost, its uplinksynchronization. Once a user equipment has achieved uplinksynchronization, the base station can schedule uplink transmissionresources for it. One scenario relevant for random access is where auser equipment in RRC_CONNECTED state, handing over from its currentserving cell to a new target cell, performs the Random Access Procedurein order to achieve uplink time-synchronization in the target cell.

There can be two types of random access procedures allowing access to beeither contention based, i.e., implying an inherent risk of collision,or contention free (non-contention based).

An exemplary definition of a random access procedure can be found in3GPP TS 38.321, v15.6.0 section 5.1.

In the following, the contention-based random access procedure is beingdescribed in more detail with respect to FIG. 7. This procedure consistsof four “steps,” and thus can be termed as well 4-step RACH procedure.First, the user equipment transmits a random access preamble on thePhysical Random Access Channel (PRACH) to the base station (i.e.,message 1 of the RACH procedure). After the base station has detected aRACH preamble, it sends a Random Access Response (RAR) message (message2 of the RACH procedure) on the PDSCH (Physical Downlink Shared Channel)addressed on the PDCCH with the (Random Access) RA-RNTI identifying thetime-frequency and slot in which the preamble was detected. If multipleuser equipment transmitted the same RACH preamble in the same PRACHresource, which is also referred to as collision, they would receive thesame random access response message. The RAR message may convey thedetected RACH preamble, a timing alignment command (TA command) forsynchronization of subsequent uplink transmissions based on the timingof the received preamble, an initial uplink resource assignment (grant)for the transmission of the first scheduled transmission and anassignment of a Temporary Cell Radio Network Temporary Identifier(T-CRNTI). This T-CRNTI is used by the base station to address themobile(s) whose RACH preamble was detected until the RACH procedure isfinished, since the “real” identity of the mobile at this point is notyet known by the base station.

The user equipment monitors the PDCCH for reception of the random accessresponse message within a given time window (e.g., termed RAR receptionwindow), which can be configured by the base station. In response to theRAR message received from the base station, the user equipment transmitsthe first scheduled uplink transmission on the radio resources assignedby the grant within the random access response. This scheduled uplinktransmission conveys the actual random access procedure message like forexample an RRC Connection Request, RRC Resume Request or a buffer statusreport.

In case of a preamble collision having occurred in the first message ofthe RACH procedure, i.e., multiple user equipment have sent the samepreamble on the same PRACH resource, the colliding user equipment willreceive the same T-CRNTI within the random access response and will alsocollide in the same uplink resources when transmitting their scheduledtransmission in the third step of the RACH procedure. In case thescheduled transmission from one user equipment is successfully decodedby base station, the contention remains unsolved for the other userequipment(s). For resolution of this type of contention, the basestation sends a contention resolution message (a fourth message)addressed to the C-RNTI or Temporary C-RNTI. This concludes theprocedure.

FIG. 8 is illustrating the contention-free random access procedure,which is simplified in comparison to the contention-based random accessprocedure. The base station provides in a first step the user equipmentwith the preamble to use for random access so that there is no risk ofcollisions, i.e., multiple user equipment transmitting the samepreamble. Accordingly, the user equipment is subsequently sending thepreamble that was signaled by the base station in the uplink on a PRACHresource. Since the case that multiple UEs are sending the same preambleis avoided for a contention-free random access, essentially, acontention-free random access procedure is finished after havingsuccessfully received the random access response by the UE.

3GPP is also studying a 2-step (contention-based) RACH procedure for 5GNR, where a message 1 (can also be termed msgA), that corresponds tomessages 1 and 3 in the four-step LTE RACH procedure, is transmitted atfirst. Then, the gNB will respond with a message 2 (can also be termedmsgB), corresponding to messages 2 and 4 of the LTE RACH procedure. ThismsgB can include, e.g., a Success random access response (RAR), aFallback RAR, and optionally a backoff indication. Some furtherassumptions are made for the 2-step RACH procedure, such as that the UE,after deciding on the RACH type (e.g., the 2-step RACH), keeps retryingthat same RACH type until failure. But there may be also the possibilitythat the UE can fallback to the 4-step RACH procedure after a certaintime.

Moreover, the network may semi-statically determine radio resources, tobe used for performing the 2-step RACH procedure and the 4-step RACHprocedure, that are exclusive from one another. The radio resources usedfor transmitting the first message in the RACH procedure include atleast the RACH occasion as well as the preambles. For instance, in the2-step RACH procedure, the first message msgA uses not only the PRACHresource (e.g., the RACH occasion and preamble) but also the associatedPUSCH resources.

Due to the reduced message exchange, the latency of the 2-step RACHprocedure may be reduced compared to the 4-step RACH procedure. On theother hand, the 2-step RACH can consume more radio resources than the4-step RACH procedure, because additional PUSCH resources are requiredfor the first message transmitted in the 2-step RACH procedure.

The network may, e.g., configure a UE to use only the 4-step RACH or2-step RACH or to use both the 4-step RACH and the 2-step RACH.

Consequently, there will be the possibility that a UE supports both the4-step RACH procedure and the 2-step RACH procedure. It is possible thatselecting the appropriate type of RACH procedure (e.g., 2-step vs4-step) can be based on an indication provided via system information toall UEs or could be done based on a UE-dedicated configuration for eachUE separately, e.g., using RRC configuration message(s).

The inventors have identified disadvantages with the current preliminaryagreements on how to select the type of RACH procedure that the UE is toperform.

For example, if the gNB instructs all the UEs to perform the type ofRACH procedure using system information, then the radio resources forthe instructed RACH type (e.g., 2-step) may become very congested andthe radio resources for the other RACH type (e.g., 4-step) will behardly utilized. This will have negative impact on the radio resourcemanagement as well as on the success of performing the random accessprocedure.

One the other hand, instructing UEs in a dedicated manner, e.g., using adedicated RRC message, may not suffer from the above-discusseddisadvantage when using system information. On the other hand, it mayonly be applicable to UEs in RRC_CONNECTED state that are actuallyconnected to the network and are able to receive such a RRC message.Other UEs (e.g., in RRC Idle) might not be able to receive suchinformation at all. This dedicated communication may further result in asignificant signaling overhead.

Consequently, the inventors have identified the possibility to improvethe random access procedure performed between the UE and the basestation, particularly in case there are several different types ofrandom access procedure.

In the following, UEs, base stations, and procedures to meet these needswill be described for the new radio access technology envisioned for the5G mobile communication systems, but which may also be used in LTEmobile communication systems. Different implementations and variantswill be explained as well. The following disclosure was facilitated bythe discussions and findings as described above and may for example bebased at least on part thereof.

In general, it should be noted that many assumptions have been madeherein so as to be able to explain the principles underlying the presentdisclosure in a clear and understandable manner. These assumptions arehowever to be understood as merely examples made herein for illustrationpurposes that should not limit the scope of the disclosure. A skilledperson will be aware that the principles of the following disclosure andas laid out in the claims can be applied to different scenarios and inways that are not explicitly described herein.

Moreover, some of the terms of the procedures, entities, layers, etc.,used in the following are closely related to LTE/LTE-A systems or toterminology used in the current 3GPP 5G standardization, even thoughspecific terminology to be used in the context of the new radio accesstechnology for the next 3GPP 5G communication systems is not fullydecided yet or might finally change. Thus, terms could be changed in thefuture, without affecting the functioning of the embodiments.Consequently, a skilled person is aware that the embodiments and theirscope of protection should not be restricted to particular termsexemplarily used herein for lack of newer or finally agreed terminologybut should be more broadly understood in terms of functions and conceptsthat underlie the functioning and principles of the present disclosure.

For instance, a mobile station or mobile node or user terminal or userequipment (UE) is a physical entity (physical node) within acommunication network. One node may have several functional entities. Afunctional entity refers to a software or hardware module thatimplements and/or offers a predetermined set of functions to otherfunctional entities of the same or another node or the network. Nodesmay have one or more interfaces that attach the node to a communicationfacility or medium over which nodes can communicate. Similarly, anetwork entity may have a logical interface attaching the functionalentity to a communication facility or medium over which it maycommunicate with other functional entities or correspondent nodes.

The term “base station” or “radio base station” here refers to aphysical entity within a communication network. As with the mobilestation, the base station may have several functional entities. Afunctional entity refers to a software or hardware module thatimplements and/or offers a predetermined set of functions to otherfunctional entities of the same or another node or the network. Thephysical entity performs some control tasks with respect to thecommunication device, including one or more of scheduling andconfiguration. It is noted that the base station functionality and thecommunication device functionality may be also integrated within asingle device. For instance, a mobile terminal may implement alsofunctionality of a base station for other terminals. The terminologyused in LTE is eNB (or eNodeB), while the currently used terminology for5G NR is gNB.

FIG. 9 illustrates a general, simplified and exemplary block diagram ofa user equipment (also termed communication device) and a schedulingdevice (here exemplarily assumed to be located in the base station,e.g., the eLTE eNB (alternatively termed ng-eNB) or the gNB in 5G NR).The UE and eNB/gNB are communicating with each other over a (wireless)physical channel respectively using the transceiver.

The communication device may comprise a transceiver and processingcircuitry. The transceiver in turn may comprise and/or function as areceiver and a transmitter. The processing circuitry may be one or morepieces of hardware such as one or more processors or any LSIs. Betweenthe transceiver and the processing circuitry there is an input/outputpoint (or node) over which the processing circuitry, when in operation,can control the transceiver, i.e., control the receiver and/or thetransmitter and exchange reception/transmission data. The transceiver,as the transmitter and receiver, may include the RF (radio frequency)front including one or more antennas, amplifiers, RFmodulators/demodulators and the like. The processing circuitry mayimplement control tasks such as controlling the transceiver to transmituser data and control data provided by the processing circuitry and/orreceive user data and control data, which is further processed by theprocessing circuitry. The processing circuitry may also be responsiblefor performing other processes such as determining, deciding,calculating, measuring, etc. The transmitter may be responsible forperforming the process of transmitting and other processes relatedthereto. The receiver may be responsible for performing the process ofreceiving and other processes related thereto, such as monitoring achannel.

An improved procedure on how to perform a random access procedure willbe described in the following.

-   -   FIG. 10 illustrates a simplified and exemplary UE structure        according to one solution of the improved procedure, and can be        implemented based on the general UE structure explained in        connection with FIG. 9. The various structural elements of the        UE illustrated in said figure can be interconnected between one        another, e.g., with corresponding input/output nodes (not        shown), e.g., in order to exchange control and user data and        other signals. Although not shown for illustration purposes, the        UE may include further structural elements.

As apparent from FIG. 10, the UE may include a random access typethreshold values receiver, a random value determining circuitry, arandom access type threshold value selecting circuitry, a valuecomparison circuitry, a random access procedure type selectingcircuitry, and a random access procedure performing circuitry.

In the present case as will become apparent from the below disclosure,the processing circuitry can thus be exemplarily configured to at leastpartly perform one or more of determining a random value, selecting oneout of plurality of the random access type threshold values, comparingthe random value with the one random access type threshold value,selecting a random access procedure type, performing a random accessprocedure, determining whether an access attempt to a radio cell can bemade or not as part of an access control procedure, etc.

The receiver can thus be exemplarily configured to at least partlyperform one or more of receiving a plurality of random access typethreshold values, receiving messages as part of a random accessprocedure, receiving information about associations between the randomaccess type threshold values and other criteria (such as the RACHtriggers, the access categories, channel qualities, radio cells), etc.

The transmitter can thus be exemplarily configured to at least partlyperform one or more of transmitting messages as part of a random accessprocedure, etc.

FIG. 11 is a sequence diagram for an exemplary UE behavior according tothe improved RACH procedure, which will be described in more detail inthe following.

It is assumed that the UE supports several types of random accessprocedures, such as the 2-step and 4-step RACH (here thecontention-based) procedures discussed above. In the following, it isexemplarily assumed that there are only two different types of randomaccess procedures the UE needs to select from. However, the improvedRACH procedure is not limited thereto, and a UE may equally select frommore than two different RACH procedures.

It is further exemplarily assumed that the UE is responsible for takingthe final decision on which type of RACH procedure it should perform,e.g., to access the radio cell. This decision may be controlled to someextent by the network operator (e.g., the gNB) by providing suitableparameters, to be used by the UE to arrive at a type of RACH procedure.

Correspondingly, the UE may receive a plurality of threshold parameters(could also be termed random access type threshold values or simply RACHtype thresholds) to then be used for selecting the RACH type. As will beexplained in more detail later, by providing a plurality of RACH typethresholds (instead of, e.g., one probability threshold), the networkcan perform an accurate and precise control of how different UEs willselect the RACH type, for instance by allowing to take into account theRACH trigger, the access category associated with the RACH procedure tobe performed, the channel quality of the radio link over which the RACHprocedure is to be performed, or the radio cell, e.g., PCell vs. SCell,over which the RACH procedure is to be performed.

Although here and in the following the use of a plurality of RACH typethresholds is assumed, it is also possible to use only one RACH typethreshold to control the RACH type selection at the UE. In this case,control of the RACH type selection may be less accurate and precise. Onthe other hand, the RACH type selection at the UE could be simplified,as well as the parameters to be configured by the network side (e.g.,transmitted by the gNB) could be reduced thereby.

According to the improved RACH procedure, the RACH type selection willbe performed based on a random value and the received RACH typethresholds. Correspondingly, the UE determines a random value. Further,the UE selects one out of the plurality of random access type thresholdvalues, and compares the previously determined random value with theselected random access type threshold value. Based on the comparisonresult, the UE selects the type of random access procedure. Then, the UEperforms the random access procedure according to the selected type.

By using this mechanism of comparing a UE-chosen random value against anetwork-defined threshold, the network can control the loading of 2-stepand/or 4-step RACH resources in a suitable way. Furthermore, thismechanism facilitates that there is no need to configure particular UEsto perform the 2-step RACH or the 4-step RACH procedure.

FIG. 12 is a sequence diagram for an exemplary gNB behavior according tothe improved RACH procedure, which will be described in more detail inthe following. The gNB can transmit information on the plurality ofrandom access type threshold values to the UE, such that the UE can usesame to perform the RACH type selection as explained above and in thefollowing. After the UE determines the type of RACH, the UE starts theRACH procedure, and the gNB can participate in the RACH procedureinitiated by the UE, e.g., accordingly receiving the 1^(st) and 3^(rd)messages and transmitting the 2^(nd) and 4^(th) messages of the 4-stepRACH (see FIG. 7 and related paragraphs above) or receiving the 1^(st)message and transmitting the 2^(nd) message of the 2-step RACH.

The random value as well as the values of the received RACH typethresholds should be coordinated in order to allow for a meaningfulcomparison. For instance, the RACH type thresholds and the random valuescould be defined as probabilities, e.g., their values being between 0and 1 (non-integer values), or between 0 and 100. Correspondingly, whendefining the probability threshold to be 0 or 1, the network ensuresthat the particular RACH type will always or never be used by the UEs inthe radio cell.

The RACH type threshold could relate to one of the types of the RACHprocedure, e.g., the 2-step RACH procedure, such that the RACH typeselection explained above allows determining whether to select that type(e.g., 2-step RACH) of RACH procedure. For instance, in case the randomvalue is lower than a first-type-related RACH threshold, the UEdetermines that the RACH procedure of the first type is to be selected.In case the random value is equal to or larger than thefirst-type-related RACH threshold, the UE determines that the RACHprocedure of the first type is not to be selected, but rather that theRACH procedure of the second type is selected. Here, because it wasexemplarily assumed that there are only two different RACH procedures(see above, 2-step RACH versus 4-step RACH), there would be no furtherneed to perform another RACH type selection procedure, because the UEcould directly determine to use the one or other RACH type (e.g.,4-step) based on a single RACH type selection.

Differentiating between more than two different RACH procedures isequally possible, although in that case it might be necessary to, e.g.,provide another RACH type threshold and/or for the UE to perform morethan one RACH type selection.

As already mentioned above, the UE can be provided with a plurality ofrandom access type threshold values, each of these being associated witha particular parameter or criterion that could be taken into account forthe RACH type selection. For instance, the network could differentiatethe RACH type selection per RACH trigger, and/or per access category,and/or per channel quality and/or per radio cell to be used, and/or someother suitable criteria.

In more detail, the RACH procedure can be triggered by different events,e.g., as listed above for an exemplary 3GPP-standard implementation. Forsome or all of these different RACH trigger events, a different RACHtype threshold value could be defined by the network and provided to theUE. Correspondingly, when performing the RACH type selection, the UEdetermines that RACH type threshold that is associated with the RACHtrigger that triggered the current RACH to be performed. Thepreviously-generated random value is then compared against thatRACH-trigger-specific RACH type threshold to decide with type of RACH isto be performed.

Which particular values would be associated with each RACH trigger canbe determined by the network, based on considerations such as howimportant or how urgent the RACH trigger is. For instance, the RACHtrigger “Request for Other SI” is less urgent than the “RRC ConnectionRe-establishment procedure,” as the latency requirement for acquiring an“Other SI” is less restrictive than the latency requirement for resumingfrom a lost RRC connection. In this sense, the network can configure theRACH type threshold values in a way that a UE is more likely to performthe 2-step RACH procedure when its RACH trigger is “RRC ConnectionRe-establishment,” and the UE is more likely to perform the 4-step RACHprocedure when its RACH trigger is “Request for Other SI.”

Moreover, the RACH procedure is closely linked to the access categoriesmentioned above in connection with the unified access control (UAC)procedure. For instance, it was exemplarily assumed that almost eachRACH is preceded by an access attempt under control of the UAC procedureperformed at the UE. The RACH trigger can thus be linked to a particularaccess category. In the following, an exemplary association between theRACH triggers and possible Access Categories is presented.

RACH trigger Associated Access Category Initial access from RRC_IDLEAC2, AC8 RRC Connection Re-establishment procedure AC8 DL or UL dataarrival during RRC_CONNECTED when UL DL = PDCCH ordering =synchronization status is “non-synchronized” contention-free; UL =AC4/5/6/7 UL data arrival during RRC_CONNECTED when there are AC4/5/6/7no PUCCH resources for SR available SR failure AC4/5/6/7 Request by RRCupon synchronous reconfiguration (e.g.,, AC8 handover) Transition fromRRC_INACTIVE AC2, AC8 To establish time alignment at SCell additionPDCCH ordering = contention- free Request for Other SI (see subclause7.3) AC8 Beam failure recovery contention-free

Thus, for instance, a UE performing a RACH procedure, triggered becauseof an initial access from RRC Idle, selects a RACH type threshold valuethat is associated with the Access Category 2 or 8 (below excerpt isfrom table further above), because the RACH attempt is a result ofRRC-level signaling.

Access Category number Conditions related to UE Type of access attempt 2All Emergency 8 All except for the MO signaling on conditions in RRClevel resulting from Access Category I other than paging

For other RACH triggers, several access categories are possible, and theUE could refer to the previously-performed UAC procedure to determinethe Access category of the access attempt.

For the purposes of this disclosure, some of the RACH triggers (such asbeam failure recovery, time alignment at SCell addition, DL data arrivalwhen non-synchronized) need not be necessarily associated with an accesscategory, because they are performed as a contention-free RACHprocedure, for which no type has to be selected (because it isexemplarily assumed that there will be only one type of contention-freeRACH procedure).

Which particular values would be associated with each access categorycan be determined by the network, based on considerations such as howimportant or how urgent the access category is. For instance, the AccessCategory 2 (Emergency) is more urgent than the Access Category 7 (MOdata that do not belong to any other Access Categories), as obviouslythe latency requirement for an emergency call should be much morerestrictive than the latency requirement of low-priority uplink traffic.In this sense, the network can configure the RACH type threshold valuesin a way that a UE is more likely to perform the 2-step RACH procedurewhen the RACH procedure is triggered by Access Category 2, and the UE ismore likely to perform the 4-step RACH procedure when the RACH procedureis triggered by Access Category 7.

As another possibility, each RACH type threshold could be associated toa channel quality (e.g., RSRP/RSRQ) value or range. In consequence, theUE thus determines (measures) the quality of the channel over which theRACH procedure will be performed (e.g., RSRP and/or RSRQ of the beam),and then determines the RACH type threshold that is associated with thedetermined channel quality. This determined channel-quality-specificRACH type threshold can then be used to compare the random valueagainst.

Which particular values would be associated with each channel qualitycan be determined by the network, based on considerations such asresource utilization efficiency. Using the 2-step RACH procedure willconsume more radio resources (PUCCH+PUSCH), and therefore failing a2-step RACH procedure will result in more penalty than failing a 4-stepRACH procedure. In this sense, network may want the successful rate ofperforming a 2-step RACH procedure to be higher than the successful rateof performing a 4-step RACH procedure. As a result, the network canconfigure the RACH type threshold values in a way that a UE is morelikely to perform the 2-step RACH procedure when the link qualitybetween the UE and gNB is good, and the UE is more likely to perform the4-step RACH procedure when the link quality between the UE and gNB isbad.

As still another possibility, each RACH type threshold could beassociated to a particular radio cell over which the RACH procedure isto be performed, such as the PCell or one of the SCell(s). Nodistinction has been made so far on the radio cell over which the RACHprocedure will be performed. For example, it is typically assumed thatthe contention-based RACH procedure is always performed over the PCell.Nevertheless, e.g., in future 3GPP releases it might be possible thatthe contention-based RACH procedure is performed over one of theconfigured one or more SCells. In such a scenario, the network could beinterested to separately control the use of the 2-step and 4-step RACHprocedures in a PCell and an SCell. Correspondingly, the network coulddefine different RACH type threshold values for the PCell and the one ormore SCells. For instance, if the RACH procedure shall be performed overone of the SCells, the UE would first determine the RACH type thresholdthat is associated with that SCell, and compare thepreviously-determined random value against that SCell-specific RACH typethreshold.

Which particular values would be associated with each radio cell can bedetermined by the network, based on considerations such that the RACHprocedures performed in PCell should have higher priority than the RACHprocedure performed in an SCell. It is because if a UE is performing aRACH procedure in an SCell, some other UEs may also want to perform theRACH procedure in the same cell that is a PCell for them. By assumingthe RACH procedure performed in a PCell is more urgent/important thanthe RACH procedure performed in an SCell, the network can configure theRACH type threshold values in a way that a UE is more likely to performthe 2-step RACH procedure when the RACH procedure is performed in PCell,and the UE is more likely to perform the 4-step RACH procedure when theRACH procedure is performed in the SCell.

Moreover, some or all of the above-discussed criteria (RACH trigger,access category, channel quality, radio cell) could be taken intoaccount for the RACH type selection, by providing RACH type thresholdsthat are associated to some or all of the above-discussed criteria. Forinstance, by providing RACH type thresholds that are associated to theaccess category as well as the type of radio cell could be beneficial.But also other combinations are equally possible, depending on theinterest of the network operator.

The above-presented associations between the RACH type thresholds andthe different criteria can be provided to the UE in different ways. Oneexemplary solution is to broadcast this association in systeminformation (e.g., in SIB1). In this way, all UEs in a radio cell willbe able to determine the association and be kept updated through thealready-established system information update mechanism in case theassociations are changed by the network.

According to one particular exemplary implementation where the RACH typethresholds are associated with different access categories, informationon this association could be transmitted together with the accessattempt threshold information. To said end, when using a 3GPP-standardspecific implementation, the corresponding information element, carriedby SIB1, and including information on the access attempt thresholds ofone particular access category (UA-BarringInfoSetList of SIB1, see 3GPP38.331) could be extended, e.g., as follows to carry information on theassociation between a RACH type threshold (here, e.g.,2stepRACH-ProbThres, as being used to determine whether or not the2-step RACH is to be used or not) and an access category.

UAC-BarringInfoSetList Information Element

-- ASN1START TAG-UAC-BARRINGINFOSETLIST-START UAC-BarringInfoSetList ::=  SEQUENCE (SIZE(1..maxBarringInfoSet) ) OF      UAC-BarringInfoSetUAC-BarringInfoSet ::=   SEQUENCE{ uac-BarringFactor  ENUMERATED {p00,p05, p10, p15, p20, p25,    p30, p40, p50, p60, p70, p75,    p80, p85,p90, p95} , 2stepRACH-ProbThres ENUMERATED {p00, p10, p20, p30, p40,   p50, p60, p70, p80, p90,    p100} , uac-BarringTime ENUMERATED {s4,s8, s16, s32, s64, s128,     s256, s512} , uac-BarringForAccessIdentity  BIT STRING (SIZE (7) ) } -- TAG-UAC-BARRINGINFOSETLIST-STOP --ASN1STOP

Different values can be defined for the RACH type threshold (here, e.g.,10 percent steps from 0 to 100), where p00 could imply that only 4-stepRACH is configured for this access category and p100 could imply thatonly 2-step RACH is configured for this access category; in this respectit is exemplarily assumed that any random value smaller than the2-step-RACH-specific threshold would lead to the use of the 2-step RACH,while any random value equal to or larger than the 2-step-RACH-specificthreshold would lead to not using the 2-step RACH, but to using the onlyother RACH type, i.e., the 4-step RACH.

In the above, the association between different RACH type thresholds andaccess categories, carried by the UAC-BarringInfoSetList informationelement, was described. Similarly, the associations of the RACH typethresholds with the other criteria (e.g., RACH Trigger, channel quality,PCell/SCell) can be transmitted in corresponding information elements,such as those presented in the following. All these information elementscan be transmitted, e.g., via system information, e.g., the SIB1.

In particular, the Trigger-RACHTypeSelect information element associatesa particular RACH Trigger event (here identified by “rach-TriggerEvent”)with a particular RACH type threshold (here identified by2stepRACH-ProbThres).

Trigger-RACHTypeSelect Information Element

ASN1START TAG-TRIGGER-- RACHTYPESELECT-START Trigger-RACHTypeSelectList::=   SEQUENCE (SIZE(1..maxRACHTypelist) )     OF Trigger-RACHTypeSelectTrigger-RACHTypeSelect ::=   SEQUENCE{  rach-TriggerEvent   BIT STRING(SIZE(X) ) ,  2stepRACH-ProbThres    ENUMERATED{p00, p10, p20, p30, p40,p50, p80, p70, p80, p90, p100} , } -- TAG-TRIGGER-RACHTYPESELECT-STOP --ASN1STOP

The ChannelQ-RACHTypeSelect information element associates differentchannel qualities (here identified by channel-Quality-UpperBound andchannel-Quality-LowerBound) with a particular RACH type threshold (hereidentified by 2stepRACH-ProbThres).

ChannelQ-RACHTypeSelect Information Element

-- ASN1START -- TAG-CHANNELQ-RACHTYPESELECT-STARTChannelQ-RACHTypeSelectList ::=  SEQUENCE (SIZE(1..maxRACHTypelist) )   OF ChannelQ-RACHTypeSelect ChannelQ-RACHTypeSelect ::=  SEQUENCE{ channel-Quality-UpperBound     INTEGER (0..127) , channel-Quality-LowerBound     INTEGER (0..127) ,  2stepRACH-ProbThres  ENUMERATED {p00, p10, p20, p30, p40, p50, p60, p70, p80, p90, p100} ,} -- TAG-CHANNELQ-RACHTYPESELECT-STOP -- ASN1STOP

The Cell-RACHTypeSelect information element associates different radiocells (here identified by cell-Type) with a particular RACH typethreshold (here identified by 2stepRACH-ProbThres).

Cell-RACHTypeSelect Information Element

----- ASN1START TAG-CELL-PACHTYPESELECT-START Cell-RACHTypeSelectList::= SEQUENCE (SIZE(1..maxRACHTypelist) ) OF     Cell-RACHTypeSelectCell-RACHTypeSelect ::= SEQUENCE{  cell-Type    ENUMERATED {PCell,SCell} ,  2stepRACH-ProbThres    ENUMERATED {p00, p10, p20, p30,   p40,p50, p60, p70, p80, p90, p100} , } -- TAG-CELL-RACHTYPESELECT-STOP --ASN1STOP

Instead of defining the threshold for the 2-step RACH procedure, it isalso possible to define a threshold for using the 4-step RACH procedureand using same in the RACH type selection in a corresponding manner. Thefollowing is an example of such a 4-step RACH threshold configuration:

4stepR-ACH-ProbThres ENUMERATED {p00, p10, p20, p30, p40, p50, p60, p70,p80, p90, p1001,

In that case for instance, any random value smaller than the4-step-RACH-specific threshold would lead to the use of the 4-step RACH,while any random value equal to or larger than the 4-step-RACH-specificthreshold would lead to not using the 4-step RACH, but to using the onlyother RACH type, i.e., the 2-step RACH.

In the following, variations of the above-described improved RACHprocedure will be described in detail. For instance, some of thesevariations revolve around the inter-relation between the UAC procedureand the RACH procedure. UAC, as currently specific in 3GPP, has beenintroduced above. In order to avoid repetitions, reference is made tothose detailed explanations and only a brief summary is presented. Insummary, the UE performs an access control procedure (UAC) to determinewhether it should make an access attempt to the radio cell or not. TheUAC check is based on the one or more access identities of the accessattempt and, in case an access attempt is not allowed based on theaccess identities, the UAC check is continued based on the accesscategory of the access attempt. As mentioned before, the UE determines arandom value and compares same against the access attempt thresholdassociated with the access category (UAC-BarringFactor). The UE isbarred from accessing the cell, e.g., in case the random value is equalto or larger than the threshold, and the UE can perform an accessattempt in case the random value is less than the threshold.

A positive access attempt check (i.e., the UE can perform an accessattempt) can be followed by a RACH procedure, e.g., according to one ofthe above improved RACH procedures. According to one exemplaryimplementation, the UAC procedure and the improved RACH procedure,although they may be subsequent, can be performed independently from oneanother. For instance, the UE performs first the UAC procedure,including—if necessary—the steps of drawing a random value and comparingsame to the appropriate access attempt threshold (e.g., theUAC-BarringFactor). Subsequently, as part of the improved RACH typeselection solutions explained above, the UE draws another random valueand compares this other random value to the appropriate RACH typethreshold to select the type of the RACH procedure to be performed.

This solution is illustrated in FIG. 13, which is a sequence diagram foran exemplary UE behavior according to the improved RACH procedure. Inline with the above explanation, the UE may have to draw random numberstwo times, one random number A during the UAC check (based on the accesscategory) and another random number B for the RACH type selection. Therespective checks are then made based on the respective random number.

Separating the two procedures from one another facilitates that the UACprocedure need not be changed. Further, the RACH type selection isindependent from the UAC procedure, such that the RACH type selectioncan be controlled independently by the network.

According to another exemplary implementation, instead of drawing arandom number two times as done for the above-solution as explained,e.g., in FIG. 13, the UAC and RACH type selection procedures areinterrelated so as to facilitate that a random number need to be drawnonly once. In particular, if a random number is already drawn as part ofthe UAC procedure, the UE may reuse that random number also for the RACHtype selection and does not draw another random number (random number Bin solution of FIG. 13). Otherwise, if no random number is drawn as partof the UAC procedure (e.g., because access attempt is allowed alreadybased on one of the access identities), then, the UE shall draw a randomnumber for selecting the RACH type.

It should be further noted that the RACH type threshold value and theaccess attempt threshold value work together to determine how many UEsaccess the cell based on a particular type of RACH procedure. Forinstance, when the RACH type threshold value is set higher than theaccess attempt threshold value, the network may achieve that the randomvalue is always lower than the RACH type threshold value, becauseexemplary only those UEs with random value<access attempt thresholdvalue perform an access attempt and thus perform the RACH typeselection. This would result in that all the UE always select the sametype of RACH procedure.

An exemplary sequence of checks is presented in the following. If theuac-BarringFor AccessIdentity-based check results in that the UE needsto check further based on the uac-BarringFactor, the UE draws a randomvalue (RAN_Value, 0 . . . 99).

If 2stepRACH-ProbThres<uac-BarringFactor

-   -   If uac-BarringFactor<=RAND_VALUE→UE is not allowed to access the        cell    -   If 2stepRACH-ProbThres<=RAND_VALUE<uac-BarringFactor→UE uses the        4-step RACH    -   If RAND_VALUE<2stepRACH-ProbThres→UE uses the 2-step RACH

If uac-BarringFactor<=2stepRACH-ProbThres

-   -   If uac-BarringFactor<=RAND_VALUE→UE is not allowed to access the        cell    -   If RAND_VALUE<uac-BarringFactor→UE uses 2-step RACH

If the uac-BarringForAccessIdentity-based check results in that the UEis allowed to access the cell, UE draws a random value (RAND_VALUE, 0 .. . 99)

-   -   If 2stepRACH-ProbThres<=RAND_VALUE→UE uses the 4-step RACH    -   If RAND_VALUE<2stepRACH-ProbThres→UE uses the 2-step RACH

One exemplary implementation of the above solution where only one randomvalue needs to be determined is illustrated in FIG. 14, which is asequence diagram for an exemplary UE behavior according to the improvedRACH procedure. As apparent therefrom, the UE needs to determine onlyone random number A, in any case. The RACH type selection is thenperformed based on this random number A that may have been already drawnand used for the access attempt check performed based on the accesscategory.

These exemplary implementations have the advantage that in any case onlyone random number needs to be drawn at the UE. Determining a random isprocessor consuming and increases the UE complexity, and it is typicallypreferred to avoid these drawbacks. Moreover, the UAC check can remainexactly the same as currently defined, because no change is actuallynecessary. For instance, the additional process of drawing a randomnumber A in case the access attempt is granted due to a matching accessidentity can be part of the RACH type selection.

FIG. 14 further illustrates an optional step of normalizing the RACHtype threshold value, which can be performed in case the access attemptis allowed based on the access identity. In more detail, assuming forinstance that the access attempt threshold value is set to 0.8, meaningthat 80% of the UE will be allowed to perform an access attempt with thecell (based on the random number A, see FIG. 14). It is furtherexemplarily assumed that the RACH type threshold value is 0.4. Keepingin mind that only those UEs with a random value A of 0-0.8 attempt theaccess, this RACH type selection results in that in effect 50% (i.e.,0.4/0.84) of those UEs attempting the access will be using, e.g., the2-step RACH. However, in case the access attempt is allowed based on theaccess identity, when having to draw a random number A, the range ofrandom values of UEs performing the RACH type selecting is between 0and 1. This results in that in effect 40% (0, 4/1) of those UEsattempting the access will be using, e.g., the 2-step RACH. Therefore,the control of the RACH type selection differs depending on how theaccess decision is allowed for the UE, be it based on the accessidentity or based on the access category.

In order to allow for a uniform control of the RACH type selection, anormalizing step can be optionally introduced, e.g., when the accessattempt is allowed based on the access identity. In particular, thenormalizing step adapts the value of the RACH type threshold such thatthe probability of selecting a particular type of RACH procedure is thesame when having been allowed to access the cell based on accessidentities and when having been allowed to access the cell based onaccess categories. The normalization is further dependent on the valueof the access attempt threshold. For instance, in the above-usedexemplary scenario, the RACH type threshold could be normalized to 0.5.In general, the normalized RACH type threshold value can be calculatedby “old RACH type threshold value”/“access attempt threshold value,” inthe above case 0.4/0.8=0.5.

As explained before, information on the association could be transmittedtogether with the access attempt threshold information. To said end,when using a 3GPP-standard specific implementation, the correspondinginformation element, carried by SIB1, and including information on theaccess attempt thresholds of one particular access category(UA-BarringInfoSetList of SIB1, see 3GPP 38.331) could be extended,e.g., as follows to carry information on the association between a RACHtype threshold (here, e.g., 2stepRACH-ProbThres, as being used todetermine whether or not the 2-step RACH is to be used or not) and anaccess category.

UAC-BarringInfoSetList Information Element

-- ASN1START -- TAG-UAC-BARRINGINFOSETLIST-START UAC-BarringInfoSetList::=  SEQUENCE (SIZE(1..maxBarringInfoSet) ) OF      UAC-BarringInfoSetUAC-BarringInfoSet ::=  SEQUENCE { uac-BarringFactor ENUMERATED {p00,p05, p10, p15, p20, p25,    p30, p40, p50, p60, p70, p75,    p80, p85,p90, p95} , 2stepRACH-ProbThres  ENUMERATED {p00, p05, p10, p15, p20,   p25, p30, p40, p50, p60, p70,    p75, p80, p85, p90, p95} ,uac-BarringTime ENUMERATED {s4, s8, s16, s32, s64, s128,     s256, s512}, uac-BarringForAccessIdentity   BIT STRING (SIZE (7) ) } --TAG-UAC-BARRINGINFOSETLIST-STOP -- ASN1STOP

In this exemplary solution, the particular values for the2-stepRACH-ProbThres are the same as for the uac-BarringFactor so as toallow the network to define the same threshold for the barring and theRACH type selection. In particular, when selecting the same RACH Typethreshold as for the access attempt threshold, the network can controlthat the UEs perform the RACH according to one type only.

According to further solutions, the network (e.g., the gNB) can changethe value of the RACH type threshold dynamically (optionally also thevalue of the access attempt threshold) and then transmit the updatedRACH type threshold (optionally also the updated access attemptthreshold) to the UEs, e.g., in the system information.

The network may consider different criteria for dynamically adapting thethreshold(s). Such criteria may involve, e.g., the loading of the radiocell or the availability of the uplink radio resources. For instance,the loading of the radio cell can be determined at the gNB, so as todetermine the appropriate value of the RACH type threshold (andoptionally of the access attempt threshold). In one exemplaryimplementation, if the cell load is high (e.g., above a particularthreshold such as there are 1000 active UEs in RRC_CONNECTED mode), theRACH type threshold could be adapted so as to allow less UEs to use the2-step RACH procedure. The 2-step RACH procedure will consume more radioresources because of the combined PRACH and PUSH transmission in thefirst message, such that in high-load situations, the available radioresource might not be sufficient to support the 2-step RACH procedure,but may still be able to support the 4-step RACH procedure. Conversely,if the cell load is low (e.g., below that same particular threshold),the RACH type threshold could be adapted so as to allow more UEs to usethe 2-step RACH procedure. The same or similar dynamic adaptation basedon the cell load can also be performed for the access attempt threshold(e.g., the uac-barringfactor).

On the other hand, the availability of uplink resources can changesignificantly from time to time. Although this is true in general, thisis particularly true for an unlicensed radio cell (e.g., NR-Uscenarios). Usage of the unlicensed bands has become a focus for the new5G-NR development. In NR, Listen-Before-Talk is to be performed onunlicensed carriers. In particular, transmitting entities perform LBT,and channel occupation is only allowed after a successful LBT ClearChannel Assessment (CCA), so as to facilitate the coexistence with othersystems, such as Wi-Fi (IEEE 802.11) systems operating at theseunlicensed bands (see, e.g., 3GPP Technical Report TR 36.889, version13.0.0).

Correspondingly, the resources may be repeatedly blocked by otherterminals or WIFI nodes, such that the availability of uplink resourcesfor the UEs controlled by the gNB is low. On the other hand, if thereare few other UEs or WiFi nodes using the unlicensed carrier, theavailability of uplink resources for the UEs controlled by the gNB ishigh. The gNB, which may also perform a CCA of its own to determine theavailability of uplink resources in its radio cell, can adapt the RACHType threshold to the changing availability. For instance, if the uplinkresources are scarce (e.g., below a particular threshold such as wherethe channel occupancy time is less than 30% of the total time), the gNBcould adapt the RACH type threshold so as to allow less UEs to use the2-step RACH procedure. Considering that the 2-step RACH procedure willconsume more radio resources than the 4-step RACH procedure, if the gNBcan hardly obtain the channel, the available radio resources will not besufficient to support the 2-step RACH, but may still be able to supportthe 4-step RACH. On the other hand, if the uplink resources are amplyavailable (e.g., above a particular threshold, such as where the channeloccupancy time is more than 90% of the total time), the RACH typethreshold could be adapted so as to allow more UEs to use the 2-stepRACH procedure.

The same or similar dynamic adaptation based on the cell load can alsobe performed for the access attempt threshold (e.g., theuac-barringfactor).

Instead of broadcasting the updated RACH type threshold (optionally alsothe updated access attempt threshold) in system information as mentionedabove, the gNB may also provide the updated values in or together with aCOT-indication (Channel Occupancy Time indication) to the UEs. The COTindication is transmitted by the gNB (in the CO-PDCCH) to indicate tothe UEs that the channel is now available. This COT indication can beextended further so as to carry information on the updated values of oneor both of the RACH type threshold and the access attempt threshold. Ifthe UE receives the updated values via the CO-PDCCH, the previous valuesreceived via system information are overwritten with the new values.

FIG. 15 illustrates a sequence diagram for an exemplary behavior of thegNB to update the RACH type threshold, according to an exemplaryimplementation. As apparent therefrom, it is assumed that the gNBconfigures a plurality of RACH type thresholds and access attemptthresholds, according to one of the above discussed solutions.Information on these thresholds is then transmitted to the UE (e.g., viasystem information) so as to be used for the RACH type selection andrespectively UAC procedure. As discussed above, in order to update thethresholds values, the gNB may monitor the cell load and theavailability of the uplink resources (in illustration of FIG. 15, termedRACH resource congestion and RACH resource clear). If there is asignificant change in any of the monitored criteria, the gNB can decideto adapt any or both of the RACH type threshold and the access attemptthreshold and transmit the updated values to the UEs (e.g., broadcastingagain in system information or in a COT, or in a dedicated manner asexplained below).

According to further exemplary implementations, the RACH type thresholdcan be provided to the UEs in still other ways, for instance in adedicated manner. In more detail, the gNB can transmit a dedicated RRCmessage to the UE, e.g., in case of a handover or conditional handoverscenario. In particular, the UE exchanges during a handover some RRCmessages with the old and new gNB. One of these RRC messages could beadapted to carry the value of the RACH type threshold, that the UE canuse for determining the type of the contention-based RACH during orshortly after the handover execution. In one exemplary implementation,this RACH type threshold value is applicable to all access categories,and further it may be valid until the UE acquires the RACH typethresholds of the target radio cell, e.g., via the system information.

Another way of transmitting the RACH type threshold value to the UEs isto use a message of the RACH procedure, e.g., in those cases where theRACH procedure fails (e.g., due to a contention). In one implementation,the 2^(nd) or 4^(th) message carrying the backoff indicator canadditionally carry the (updated) RACH type threshold value. The UE canthus perform a new RACH type selection (after the failed RACH procedure)using a different value for the subsequent RACH attempt. In oneexemplary implementation, this RACH type threshold value is applicableto all access categories, and further it may be valid until the UEacquires the RACH type thresholds of the radio cell, e.g., via thesystem information.

These solutions are beneficial if the network needs to alleviate the2-step or 4-step RACH radio resources in a short time. Using systeminformation to update the RACH type threshold values can be done inparallel so as to reach all UEs in the radio cell, but it may takelonger because the system information update is typically executed inthe next system information modification period.

Further Aspects

According to a first aspect, a user equipment, UE, comprising areceiver, which receives a plurality of random access type thresholdvalues. The UE further comprises processing circuitry, which determinesa random value. The processing circuitry selects a type of a randomaccess procedure to be performed by the UE, wherein the selectingcomprises at least

-   -   selecting one out of the plurality of random access type        threshold values,    -   comparing the determined random value against the selected        random access type threshold value, and    -   selecting a type of the random access procedure based on the        result of the comparison. The UE performs the random access        procedure of the selected type.

According to a second aspect provided in addition to the first aspect,the processing circuitry determines whether an access attempt to a radiocell can be made or not. In an optional implementation, the accessattempt involves performing the random access procedure. In a furtheroptional implementation, the access attempt is associated with one ormore access identities and one access category, wherein the processingcircuitry determines whether the access attempt to the radio cell can bemade or not:

-   -   first based on the one or more access identities and    -   then, if the access attempt cannot be made based on the one or        more access identities, based on the access category, wherein        determining whether the access attempt can be made or not based        on the access category involves determining an access attempt        threshold value, that is associated with the access category of        the access attempt.

According to a third aspect provided in addition to the second aspect,determining whether the access attempt can be made or not involvesdetermining a second random value and comparing the second random valueagainst the access attempt threshold value.

According to a fourth aspect provided in addition to the second aspect,determining whether the access attempt can be made or not involvescomparing the same random value, to be used for selecting the randomaccess procedure type, against the access attempt threshold value. In anoptional implementation, in case of determining that the access attemptcan be made based on the one or more access identities, selecting therandom access procedure type involves normalizing the random access typethreshold value based on the access attempt threshold value, such thatfor example a probability of performing the random access procedure ofone type in case of a successful attempt based on the access identity isthe same or similar as a probability of performing the random accessprocedure of the same one type in case of a successful attempt based onthe access category.

According to a fifth aspect, provided in addition to one of the first tofourth aspects, the plurality of random access type threshold valuesrelate to the use of one of the various types of the random accessprocedure, such as a 2-step random access procedure or a 4-step randomaccess procedure. In an optional implementation, the random value beinglower than the random access type threshold value is associated with afirst type of the random access procedure, and wherein the random valuebeing larger or equal to the random access type threshold value isassociated with a second type of the random access procedure. In anoptional implementation, the random value is a non-integer valuedetermined between 0 and 1, and the random access type threshold is alsoa non-integer value between 0 and 1.

According to a sixth aspect, provided in addition to one of the first tofifth aspects, among the plurality of random access type thresholdvalues there is one random access type threshold value associated witheach of different random access trigger events that trigger the UE toperform a random access procedure, wherein selecting the one randomaccess type threshold value involves determining the random access typethreshold value that is associated with the random access trigger thattriggered the random access procedure to be performed. Additionally oralternatively, among the plurality of random access type thresholdvalues there is one random access type threshold value associated witheach of different access categories of an access attempt, whereinselecting the one random access type threshold value involvesdetermining the random access type threshold value that is associatedwith the access category of the access attempt. Additionally oralternatively, among the plurality of random access type thresholdvalues there is one random access type threshold value associated witheach of different set of channel qualities, wherein selecting the onerandom access type threshold value involves 1) determining the channelquality of a radio link between the UE and a base station via which therandom access procedure is to be performed, and 2) determining therandom access type threshold value that is associated with thedetermined channel quality. Additionally or alternatively, among theplurality of random access type threshold values there is one randomaccess type threshold value associated with each of different radiocells of a base station, and wherein selecting the one random accesstype threshold value involves determining the random access typethreshold value associated with the radio cell over which the randomaccess procedure is to be performed, optionally wherein the differentradio cells are a primary radio cell and one or more secondary radiocells.

According to a seventh aspect provided in addition to the sixth aspect,the receiver, when in operation, receives a system information broadcastfrom a base station in a radio cell, wherein the system informationincludes one or more of:

-   -   information on an association between the random access type        threshold value and the random access trigger event,    -   information on an association between the random access type        threshold value and the access category, optionally together        with information on an association between the access attempt        threshold value and the access category,    -   information on an association between the random access type        threshold value and the channel quality,    -   information on an association between the random access type        threshold value and the radio cell over which the random access        procedure is to be performed.

According to an eighth aspect provided in addition to one of the firstto seventh aspects, the receiver receives a single random accessthreshold value from a base station in a radio cell to be used forselecting a type of random access procedure instead of using one out ofthe plurality of random access type threshold values. In an optionalimplementation, the single random access threshold value is received ina message of a failed random access procedure performed between the basestation and the UE, optionally in a random access response of the failedrandom access procedure, or in a message of a handover procedureperformed by the UE with a source and target base station.

According to a ninth aspect provided in addition to one of the first toeighth aspects, the random access procedure is one of a 2-step randomaccess procedure and a 4-step random access procedure. In one optionalimplementation, the 2-step random access procedure at least involvesthat:

-   -   a transmitter of the UE transmits a random access preamble and        uplink data to a base station,    -   the receiver receives a random access response and at least the        information on a contention resolution.

The 4-step random access procedure at least involves that:

-   -   a transmitter of the UE transmits a random access preamble to a        base station,    -   the receiver receives a random access response, indicating radio        resources to be used by the UE,    -   the transmitter transmits uplink data using the indicated radio        resources,    -   the receiver receives information on a contention resolution.

According to a tenth aspect, a method is provided comprising thefollowing steps performed by a user equipment, UE:

-   -   receiving a plurality of random access type threshold values,    -   determining a random value,    -   selecting a type of a random access procedure to be performed by        the UE, wherein the selecting comprises at least        -   selecting one out of the plurality of random access type            threshold values,        -   comparing the determined random value against the selected            random access type threshold value, and        -   selecting a type of the random access procedure based on the            result of the comparison,            performing the random access procedure of the selected type.

According to an eleventh aspect, provided in addition to the tenthaspect, the method further comprises the step of determining whether anaccess attempt to a radio cell can be made or not. In an optionalimplementation the access attempt involves performing the random accessprocedure. In an optional implementation, the access attempt isassociated with one or more access identities and one access category,and the determining involves determining whether the access attempt tothe radio cell can be made or not:

-   -   first based on the one or more access identities and    -   then, if the access attempt cannot be made based on the one or        more access identities, based on the access category, wherein        determining whether the access attempt can be made or not based        on the access category involves determining an access attempt        threshold value, that is associated with the access category of        the access attempt.

According to a twelfth aspect, provided in addition to the eleventhaspect, determining whether the access attempt can be made or notinvolves determining a second random value and comparing the secondrandom value against the access attempt threshold value.

According to a thirteenth aspect, provided in addition to the eleventhaspect, determining whether the access attempt can be made or notinvolves comparing the same random value, to be used for selecting therandom access procedure type, against the access attempt thresholdvalue. In an optional implementation, in case of determining that theaccess attempt can be made based on the one or more access identities,selecting the random access procedure type involves normalizing therandom access type threshold value based on the access attempt thresholdvalue, such that for example a probability of performing the randomaccess procedure of one type in case of a successful attempt based onthe access identity is the same or similar as a probability ofperforming the random access procedure of the same one type in case of asuccessful attempt based on the access category.

According to a fourteenth aspect, provided in addition to any of thetenth to thirteenth aspects, the plurality of random access typethreshold values relate to the use of one of the various types of therandom access procedure, such as a 2-step random access procedure or a4-step random access procedure. In an optional implementation, therandom value being lower than the random access type threshold value isassociated with a first type of the random access procedure, and whereinthe random value being larger or equal to the random access typethreshold value is associated with a second type of the random accessprocedure. In an optional implementation, the random value is anon-integer value determined between 0 and 1, and the random access typethreshold is also a non-integer value between 0 and 1.

According to a fifteenth aspect, provided in additional to any of thetenth to fourteenth aspects, among the plurality of random access typethreshold values there is one random access type threshold valueassociated with each of different random access trigger events thattrigger the UE to perform a random access procedure, wherein selectingthe one random access type threshold value involves determining therandom access type threshold value that is associated with the randomaccess trigger that triggered the random access procedure to beperformed. Additionally or alternatively, among the plurality of randomaccess type threshold values there is one random access type thresholdvalue associated with each of different access categories of an accessattempt, wherein selecting the one random access type threshold valueinvolves determining the random access type threshold value that isassociated with the access category of the access attempt.

Additionally or alternatively, among the plurality of random access typethreshold values there is one random access type threshold valueassociated with each of different set of channel qualities, whereinselecting the one random access type threshold value involves 1)determining the channel quality of a radio link between the UE and abase station via which the random access procedure is to be performed,and 2) determining the random access type threshold value that isassociated with the determined channel quality. Additionally oralternatively, among the plurality of random access type thresholdvalues there is one random access type threshold value associated witheach of different radio cells of a base station, and wherein selectingthe one random access type threshold value involves determining therandom access type threshold value associated with the radio cell overwhich the random access procedure is to be performed, optionally whereinthe different radio cells are a primary radio cell and one or moresecondary radio cells.

Hardware and Software Implementation of the Present Disclosure

The present disclosure can be realized by software, hardware, orsoftware in cooperation with hardware. Each functional block used in thedescription of each embodiment described above can be partly or entirelyrealized by an LSI such as an integrated circuit, and each processdescribed in the each embodiment may be controlled partly or entirely bythe same LSI or a combination of LSIs. The LSI may be individuallyformed as chips, or one chip may be formed so as to include a part orall of the functional blocks. The LSI may include a data input andoutput coupled thereto. The LSI here may be referred to as an IC(integrated circuit), a system LSI, a super LSI, or an ultra LSIdepending on a difference in the degree of integration. However, thetechnique of implementing an integrated circuit is not limited to theLSI and may be realized by using a dedicated circuit, a general-purposeprocessor, or a special-purpose processor. In addition, a FPGA (FieldProgrammable Gate Array) that can be programmed after the manufacture ofthe LSI or a reconfigurable processor in which the connections and thesettings of circuit cells disposed inside the LSI can be reconfiguredmay be used. The present disclosure can be realized as digitalprocessing or analogue processing. If future integrated circuittechnology replaces LSIs as a result of the advancement of semiconductortechnology or other derivative technology, the functional blocks couldbe integrated using the future integrated circuit technology.Biotechnology can also be applied.

The present disclosure can be realized by any kind of apparatus, deviceor system having a function of communication, which is referred to as acommunication apparatus.

Some non-limiting examples of such a communication apparatus include aphone (e.g., cellular (cell) phone, smart phone), a tablet, a personalcomputer (PC) (e.g., laptop, desktop, netbook), a camera (e.g., digitalstill/video camera), a digital player (digital audio/video player), awearable device (e.g., wearable camera, smart watch, tracking device), agame console, a digital book reader, a telehealth/telemedicine (remotehealth and medicine) device, and a vehicle providing communicationfunctionality (e.g., automotive, airplane, ship), and variouscombinations thereof.

The communication apparatus is not limited to be portable or movable,and may also include any kind of apparatus, device or system beingnon-portable or stationary, such as a smart home device (e.g., anappliance, lighting, smart meter, control panel), a vending machine, andany other “things” in a network of an “Internet of Things (IoT).

The communication may include exchanging data through, for example, acellular system, a wireless LAN system, a satellite system, etc., andvarious combinations thereof.

The communication apparatus may comprise a device such as a controlleror a sensor, which is coupled to a communication device performing afunction of communication described in the present disclosure. Forexample, the communication apparatus may comprise a controller or asensor that generates control signals or data signals, which are used bya communication device performing a communication function of thecommunication apparatus.

The communication apparatus also may include an infrastructure facility,such as a base station, an access point, and any other apparatus, deviceor system that communicates with or controls apparatuses such as thosein the above non-limiting examples.

Further, the various embodiments may also be implemented by means ofsoftware modules, which are executed by a processor or directly inhardware. Also a combination of software modules and a hardwareimplementation may be possible. The software modules may be stored onany kind of computer readable storage media, for example RAM, EPROM,EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc. It shouldbe further noted that the individual features of the differentembodiments may individually or in arbitrary combination be subjectmatter to another embodiment.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present disclosure asshown in the specific embodiments. The present embodiments are,therefore, to be considered in all respects to be illustrative and notrestrictive.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A user equipment (UE) comprising: a receiver, which in operation,receives a plurality of random access type threshold values, processingcircuitry, which in operation, determines a random value, the processingcircuitry, which in operation, selects a type of a random accessprocedure to be performed by the UE, wherein the selecting comprises atleast selecting one out of the plurality of random access type thresholdvalues, comparing the determined random value against the selectedrandom access type threshold value, and selecting a type of the randomaccess procedure based on the result of the comparison, wherein the UEperforms the random access procedure of the selected type.
 2. The userequipment according to claim 1, wherein the processing circuitry, whenin operation, determines whether an access attempt to a radio cell canbe made or not, wherein the access attempt involves performing therandom access procedure, wherein the access attempt is associated withone or more access identities and one access category, wherein theprocessing circuitry determines whether the access attempt to the radiocell can be made or not: first based on the one or more accessidentities and then, if the access attempt cannot be made based on theone or more access identities, based on the access category, whereindetermining whether the access attempt can be made or not based on theaccess category involves determining an access attempt threshold value,that is associated with the access category of the access attempt. 3.The user equipment according to claim 2, wherein determining whether theaccess attempt can be made or not involves determining a second randomvalue and comparing the second random value against the access attemptthreshold value.
 4. The user equipment according to claim 2, whereindetermining whether the access attempt can be made or not involvescomparing the same random value, to be used for selecting the randomaccess procedure type, against the access attempt threshold value,wherein in case of determining that the access attempt can be made basedon the one or more access identities, selecting the random accessprocedure type involves normalizing the random access type thresholdvalue based on the access attempt threshold value, such that for examplea probability of performing the random access procedure of one type incase of a successful attempt based on the access identity is the same orsimilar as a probability of performing the random access procedure ofthe same one type in case of a successful attempt based on the accesscategory.
 5. The user equipment according to claim 1, wherein theplurality of random access type threshold values relate to the use ofone of the various types of the random access procedure, such as a2-step random access procedure or a 4-step random access procedure, andwherein the random value being lower than the random access typethreshold value is associated with a first type of the random accessprocedure, and wherein the random value being larger or equal to therandom access type threshold value is associated with a second type ofthe random access procedure, the random value is a non-integer valuedetermined between 0 and 1, and the random access type threshold is alsoa non-integer value between 0 and
 1. 6. The user equipment according toclaim 1, wherein among the plurality of random access type thresholdvalues there is one random access type threshold value associated witheach of different random access trigger events that trigger the UE toperform a random access procedure, wherein selecting the one randomaccess type threshold value involves determining the random access typethreshold value that is associated with the random access trigger thattriggered the random access procedure to be performed, and/or whereinamong the plurality of random access type threshold values there is onerandom access type threshold value associated with each of differentaccess categories of an access attempt, wherein selecting the one randomaccess type threshold value involves determining the random access typethreshold value that is associated with the access category of theaccess attempt, and/or wherein among the plurality of random access typethreshold values there is one random access type threshold valueassociated with each of different set of channel qualities, whereinselecting the one random access type threshold value involves 1)determining the channel quality of a radio link between the UE and abase station via which the random access procedure is to be performed,and 2) determining the random access type threshold value that isassociated with the determined channel quality, and/or wherein among theplurality of random access type threshold values there is one randomaccess type threshold value associated with each of different radiocells of a base station, and wherein selecting the one random accesstype threshold value involves determining the random access typethreshold value associated with the radio cell over which the randomaccess procedure is to be performed, wherein the different radio cellsare a primary radio cell and one or more secondary radio cells.
 7. Theuser equipment according to claim 6, wherein the receiver, when inoperation, receives a system information broadcast from a base stationin a radio cell, wherein the system information includes one or more of:information on an association between the random access type thresholdvalue and the random access trigger event, information on an associationbetween the random access type threshold value and the access category,together with information on an association between the access attemptthreshold value and the access category, information on an associationbetween the random access type threshold value and the channel quality,information on an association between the random access type thresholdvalue and the radio cell over which the random access procedure is to beperformed.
 8. The user equipment according to claim 1, wherein thereceiver, when in operation, receives a single random access thresholdvalue from a base station in a radio cell to be used for selecting atype of random access procedure instead of using one out of theplurality of random access type threshold values, and wherein the singlerandom access threshold value is received in a message of a failedrandom access procedure performed between the base station and the UE,in a random access response of the failed random access procedure, or ina message of a handover procedure performed by the UE with a source andtarget base station.
 9. The user equipment according to claim 1, whereinthe random access procedure is one of a 2-step random access procedureand a 4-step random access procedure, wherein for the 2-step randomaccess procedure at least involves that: a transmitter of the UE, whenin operation, transmits a random access preamble and uplink data to abase station, the receiver, when in operation, receives a random accessresponse and at least the information on a contention resolution, andwherein for the 4-step random access procedure at least involves that: atransmitter of the UE, when in operation, transmits a random accesspreamble to a base station, the receiver, when in operation, receives arandom access response, indicating radio resources to be used by the UE,the transmitter, when in operation, transmits uplink data using theindicated radio resources, the receiver, when in operation, receivesinformation on a contention resolution.
 10. A method comprising thefollowing steps performed by a user equipment (UE): receiving aplurality of random access type threshold values, determining a randomvalue, selecting a type of a random access procedure to be performed bythe UE, wherein the selecting comprises at least selecting one out ofthe plurality of random access type threshold values, comparing thedetermined random value against the selected random access typethreshold value, and selecting a type of the random access procedurebased on the result of the comparison, performing the random accessprocedure of the selected type.
 11. The method according to claim 10,further comprising the step of determining whether an access attempt toa radio cell can be made or not, wherein the access attempt involvesperforming the random access procedure, wherein the access attempt isassociated with one or more access identities and one access category,and the determining involves determining whether the access attempt tothe radio cell can be made or not: first based on the one or more accessidentities and then, if the access attempt cannot be made based on theone or more access identities, based on the access category, whereindetermining whether the access attempt can be made or not based on theaccess category involves determining an access attempt threshold value,that is associated with the access category of the access attempt. 12.The method according to claim 11, wherein determining whether the accessattempt can be made or not involves determining a second random valueand comparing the second random value against the access attemptthreshold value.
 13. The method according to claim 11, whereindetermining whether the access attempt can be made or not involvescomparing the same random value, to be used for selecting the randomaccess procedure type, against the access attempt threshold value,wherein in case of determining that the access attempt can be made basedon the one or more access identities, selecting the random accessprocedure type involves normalizing the random access type thresholdvalue based on the access attempt threshold value, such that for examplea probability of performing the random access procedure of one type incase of a successful attempt based on the access identity is the same orsimilar as a probability of performing the random access procedure ofthe same one type in case of a successful attempt based on the accesscategory.
 14. The method according to claim 10, wherein the plurality ofrandom access type threshold values relate to the use of one of thevarious types of the random access procedure, such as a 2-step randomaccess procedure or a 4-step random access procedure, and wherein therandom value being lower than the random access type threshold value isassociated with a first type of the random access procedure, and whereinthe random value being larger or equal to the random access typethreshold value is associated with a second type of the random accessprocedure, the random value is a non-integer value determined between 0and 1, and the random access type threshold is also a non-integer valuebetween 0 and
 1. 15. The method according to claim 10, wherein among theplurality of random access type threshold values there is one randomaccess type threshold value associated with each of different randomaccess trigger events that trigger the UE to perform a random accessprocedure, wherein selecting the one random access type threshold valueinvolves determining the random access type threshold value that isassociated with the random access trigger that triggered the randomaccess procedure to be performed, and/or wherein among the plurality ofrandom access type threshold values there is one random access typethreshold value associated with each of different access categories ofan access attempt, wherein selecting the one random access typethreshold value involves determining the random access type thresholdvalue that is associated with the access category of the access attempt,and/or wherein among the plurality of random access type thresholdvalues there is one random access type threshold value associated witheach of different set of channel qualities, wherein selecting the onerandom access type threshold value involves 1) determining the channelquality of a radio link between the UE and a base station via which therandom access procedure is to be performed, and 2) determining therandom access type threshold value that is associated with thedetermined channel quality, and/or wherein among the plurality of randomaccess type threshold values there is one random access type thresholdvalue associated with each of different radio cells of a base station,and wherein selecting the one random access type threshold valueinvolves determining the random access type threshold value associatedwith the radio cell over which the random access procedure is to beperformed, wherein the different radio cells are a primary radio celland one or more secondary radio cells.